Locking differential with electromagnetic actuator

ABSTRACT

A differential assembly includes a case, a pair of pinion gears, a pair of side gears and an electrically operable coupling including an electromagnet. The coupling selectively drivingly interconnects one of the side gears and the case. The electromagnet of the coupling is axially moveable within the case to selectively place the differential assembly in an open or a locked condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/674,024, filed on Sep. 29, 2003.

BACKGROUND OF THE INVENTION

The present invention generally relates to differentials for motorvehicles and, more particularly, to a locking differential employing anelectromagnet to control operation of the differential.

As is known, many motor vehicles are equipped with driveline systemsincluding differentials which function to drivingly interconnect aninput shaft and a pair of output shafts. The differential functions totransmit drive torque to the output shafts while permitting speeddifferentiation between the output shafts.

Conventional differentials, such as a parallel-axis helicaldifferential, include a pair of side gears fixed for rotation with theoutput shafts and two or more sets of meshed pinion gears mounted withina differential case. However, the conventional differential mechanismhas a deficiency when a vehicle is operated on a slippery surface. Whenone wheel of the vehicle is on a surface having a low coefficient offriction, most or all of the torque will be delivered to the slippingwheel. As a result, the vehicle often becomes immobilized. To overcomethis problem, it is known to provide a mechanical differential where anadditional mechanism limits or selectively prevents differentiation ofthe speed between the output shafts. Typically, the mechanical device toprovide the limited-slip or non-slip function is a friction clutch. Thefriction clutch is a passive device which limits the differential speedbetween the output shafts only after a certain differential speed hasbeen met. Additionally, such mechanical devices may not be selectivelydisengaged during operation of anti-lock braking systems or vehicletraction control systems. For example, four-wheel anti-lock brakingsystems attempt to measure and control the rotational speed of eachwheel independently. If a mechanical type limited slip differential ispresent, independent control of the speed of each wheel coupled to adifferential is no longer possible. Accordingly, it would be desirableto provide an improved differential which may be actively controlled inconjunction with other control systems present on the vehicle.

SUMMARY OF THE INVENTION

The present invention relates to a differential system including a case,a pair of pinion gears, a pair of side gears and an electricallyoperable coupling including an electromagnet. The coupling selectivelydrivingly interconnects one of the side gears and the case. In oneinstance, the present invention includes an axially moveable actuatorhaving an electromagnet. The electromagnet may be selectively actuatedto move a ring into engagement with one of the side gears of thedifferential. In this manner, the differential may function as an “open”differential when the ring is disconnected from the side gear or as a“locked” differential when the ring engages the side gear thereby fixingthe side gear to the case.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic view of an exemplary motor vehicle drivetrainincluding a differential assembly of the present invention;

FIG. 2 is an end view of a first embodiment differential assembly of thepresent invention;

FIG. 3 is a cross-sectional side view of the differential of the presentinvention;

FIG. 4 is an end view of a second embodiment differential assembly ofthe present invention;

FIG. 5 is a cross-sectional side view of the second embodiment of thepresent invention;

FIG. 6 is a cross-sectional end view of the second embodimentdifferential assembly;

FIG. 7 is a cross-sectional side view of another embodiment of thepresent invention;

FIG. 8 is a plan view of a non-magnetizable washer used in conjunctionwith the first and second embodiments of the present invention;

FIG. 9 is a side view of the washer depicted in FIG. 8;

FIG. 10 is perspective view of a actuating ring assembly for use in theembodiment depicted in FIG. 7; and

FIG. 11 is another perspective view of the actuating ring assemblydepicted in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to an improved differential for adrivetrain of a motor vehicle. The differential of the present inventionincludes an actuator operable to place the differential in an “open” or“locked” condition. It should be appreciated that the differential ofthe present invention may be utilized with a wide variety of drivelinecomponents and is not intended to be specifically limited to theparticular application described herein. In addition, the actuator ofthe differential of the present invention may be used in conjunctionwith many types of differentials such as a bevel gear design which areof a completely open or limited-slip variety.

With reference to FIG. 1, a drivetrain 10 for an exemplary motor vehicleis shown to include an engine 12, a transmission 14, having an outputshaft 16 and a propeller shaft 18 connecting output shaft 16 to a pinionshaft 20 of a rear axle assembly 22. Rear axle assembly 22 includes anaxle housing 24, a differential assembly 26 supported in axle housing 24and a pair of axle shafts 28 and 30 respectively interconnected to leftand right and rear wheels 32 and 34. Pinion shaft 20 has a pinion gear36 fixed thereto which drives a ring gear 38 that is fixed to adifferential case 40 of differential assembly 26. A gearset 41 supportedwithin differential case 40 transfers rotary power from differentialcase 40 to axle shafts 28 and 30, and facilitates relative rotation(i.e., differentiation) therebetween. Thus, rotary power from engine 12is transmitted to axle shafts 28 and 30 for driving rear wheels 32 and34 via transmission 14, propeller shaft 18, pinion shaft 20,differential case 40 and gearset 41. While differential assembly 26 isdepicted in a rear-wheel drive application, the present invention iscontemplated for use in differential assemblies installed in trailingaxles, transaxles for use in front-wheel drive vehicles, transfer casesfor use in four-wheel drive vehicles and/or any other known vehiculardriveline application.

FIGS. 2 and 3 depict differential assembly 26 including differentialcase 40 and gearset 41. Gearset 41 includes a pair of pinion gears 42rotatably supported on a cross shaft 44. First and second side gears 45and 46 are drivingly interconnected to pinion gears 42 and axle shafts28 and 30. Differential assembly 26 also includes an actuator assembly50 operable to selectively couple side gear 45 to differential case 40,thereby placing differential assembly 26 in a fully locked condition.

A cap 48 is coupled to differential case 40 to define a pocket 49 forreceipt of actuator assembly 50. Actuator assembly 50 includes asolenoid assembly 52, an actuating ring 54, a draw plate 56, and aretainer 58. Cap 48 includes a flange 60 coupled to a flange 62 of case40. Flange 60 of cap 48 includes a recess 64 sized to receive solenoidassembly 52 during actuation. Cap 48 includes a pair of stepped bores 66and 68 which define pocket 49. Specifically, first bore 66 includes anannular surface 70 while second bore 68 includes an annular surface 72.First bore 66 includes an end face 74 radially inwardly extending fromannular surface 70. An aperture 76 extends through the cap 48 and is incommunication with second bore 68 where aperture 76 and second bore 68are sized to receive the portion of the axle shaft.

Actuating ring 54 includes a generally hollow cylindrical body 78 havingan annular recess 80 formed at one end. Side gear 45 includes asimilarly sized annular recess 82 formed in an outboard face 84. Acompression spring 85 is positioned between actuating ring 54 and sidegear 45 within annular recesses 80 and 82. A plurality of axiallyextending dogs 86 protrude from an end face 88 of actuating ring 54. Acorresponding plurality of dogs 90 axially extend from face 84 of sidegear 45. Actuating ring 54 is moveable from a disengaged position asshown in FIG. 3 to an engaged position (not shown). In the disengagedposition, dogs 86 of actuating ring 54 are released from engagement withdogs 90 of side gear 45. In contrast, when actuating ring 54 is moved toits engaged position, dogs 86 engage dogs 90 to rotatably fix side gear45 to differential case 40.

Solenoid assembly 52 includes a metallic cup 94 and a coil of wire 96.The wire is positioned within cup 94 and secured thereto by an epoxy 98.Cup 94 includes an inner annular wall 100, an outer annular wall 102 andan end wall 104 interconnecting annular walls 100 and 102. Retainer 58is a substantially disc-shaped member having an outer edge 106 mountedto end wall 104 of cup 94. Retainer 58 is spaced apart from end wall 104to define a slot 108. Draw plate 56 is positioned within slot 108 andcoupled to actuating ring 54 via a plurality of fasteners 110. A washer112 is positioned between cap 48 and actuating ring 54. Preferably,washer 112 is constructed from a non-ferromagnetic material so as toreduce any tendency for actuating ring 54 to move toward end face 74 ofmetallic cap 48 instead of differential case 40 during energization ofsolenoid assembly 52. A bearing 114 supports cup 94 on an outer journal116 of cap 48.

Coil 96 is coupled to a controller 118 (FIG. 1) which operates toselectively energize and de-energize coil 96. During coil energization,a magnetic field is generated by current passing through coil 96. Themagnet field causes actuator assembly 50 to be drawn toward flange 60 ofcap 48. As solenoid assembly 52 enters recess 64, dogs 86 of actuatingring 54 engage dogs 90 of side gear 45. Once the dogs are engaged,actuating ring 54 is in its engaged position and differential assembly26 is in a fully locked condition. One skilled in the art willappreciate that the axially moveable electromagnet of the presentinvention provides a simplified design having a reduced number ofcomponents. Additionally, the present invention utilizes the entiredifferential case as the armature for the electromagnet. This allows amore efficient use of the available magnetic force. These features allowa designer to reduce the size of the electromagnet because the armaturemore efficiently utilizes the electromotive force supplied by theelectromagnet. Such a compact design allows for minor modification ofpreviously used components and packaging with a standard sized axlehousing.

To place differential assembly 26 in the open, unlocked condition,current is discontinued to coil 96. The magnetic field ceases to existonce current to coil 96 is stopped. At this time, compression in spring85 causes actuator assembly 50 to axially translate and disengage dogs86 from dogs 90. Accordingly, side gear 45 is no longer drivinglycoupled to differential case 40, thereby placing differential assembly26 in the open condition. It should also be appreciated that actuationand deactuation times are very short due to the small number of movingcomponents involved. Specifically, no relative ramping or actuation ofother components is required to cause engagement or disengagement ofdogs 86 and dogs 90.

Electronic controller 118 controls the operation of actuator assembly50. Electronic controller 118 is in receipt of data collected by a firstspeed sensor 120 and a second speed sensor 122. First speed sensor 120provides data corresponding to the rotational speed of axle shaft 28.Similarly, second speed sensor 122 measures the rotational speed of axleshaft 30 and outputs a signal to controller 118 indicative thereof.Depending on the data collected at any number of vehicle sensors such asa gear position sensor 124, a vehicle speed sensor 126, a transfer caserange position sensor or a brake sensor 128, controller 118 willdetermine if an electrical signal is sent to coil 96. Controller 118compares the measured or calculated parameters to predetermined valuesand outputs an electrical signal to place differential assembly 26 inthe locked position only when specific conditions are met. As such,controller 118 assures that an “open” condition is maintained whenevents such as anti-lock braking occur. Limiting axle differentiationduring anti-lock braking would possibly counteract the anti-lock brakingsystem. Other such situations may be programmed within controller 118.

FIGS. 4-6 depict an alternate embodiment differential assembly 200.Differential assembly 200 is substantially similar to differentialassembly 26 except that differential assembly 200 relates to a parallelaxis helical differential. Accordingly, like elements will retain thereference numerals previously introduced.

Differential assembly 200 includes a planetary gearset 202 which isoperable for transferring drive torque from differential case 40 to axleshafts 28 and 30 in a manner facilitating speed differential and torquebiasing therebetween. Gearset 202 includes a pair of helical side gears204 and 206 having internal splines that are adapted to mesh withexternal splines on corresponding end segments of axle shafts 28 and 30.In addition, side gears 204 and 206 respectively include hubs 208 and210 which are seated in corresponding annular sockets 212 and 214. Sidegear 204 also includes a plurality of axially extending dogs 215.Gearset 202 further includes a spacer block 216 for maintaining sidegears 204 and 206 and axle shafts 28 and 30 in axially spaced relationto each other. Once installed, spacer block 216 is free to rotate withrespect to either axle shaft 28 and 30 and differential case 40.

Planetary gearset 202 also includes a first set of helical pinions 218journally supported in first gear pockets 220 formed in differentialcase 40. A set of second helical pinions 222 are journally supported insecond gear pockets 224 formed in differential case 40. While notlimited thereto, differential 200 is shown to include three firstpinions 218 and three second pinions 222 arranged in meshed pairs,referred to as meshed pinion sets. Gear pockets 220 and 224 arelongitudinally extending, elongated, partially cylindrical bores and areformed in paired overlapping sets such that they communicate with aninterior volume of differential case 40.

First pinions 218 are shown to include a long, larger diameter gearsegment 230 and a short, smaller diameter stub shaft segment 232. Wheninstalled in first gear pockets 220, first pinions 218 are arranged suchthat the teeth of gear segments 230 are meshed with the teeth of sidegear 204 while their outer diameter tooth end surfaces are journallysupported by the bearing wall surface of pockets 220.

Likewise, second pinions 222 are shown to include a long, largerdiameter gear segment 234 and a short, smaller diameter stub shaft 236.When installed in second gear pockets 224, second pinions are arrangedsuch that the teeth of gear segments 234 are meshed with the teeth ofside gear 206 while their outer diameter tooth end surfaces arejournally supported by the bearing wall surface of second gear pockets224. Since pinions 218 and 222 are arranged in meshed sets, gear segment230 of one of first pinions 218 also meshes with gear segment 234 andthe corresponding one of second pinions 222. Preferably, gear segments230 and 234 are of an axial length to effectively maintain meshedengagement substantially along their entire length.

A set of support members 238 support stub shaft sections 232 on each ofpinions 218 against the bearing wall surface of its corresponding firstgear pocket 220 and against the outer diameter tooth end surfaces ofside gear 206 and gear segment 234 of its meshed second pinion. Supportmembers 238 similarly support stub shaft segment 236 of second pinions222. A more complete description of parallel-axis gear differentials isfound in U.S. Pat. No. 6,013,004 to Gage et al. which is herebyincorporated by reference.

As previously described, actuator assembly 50 is positioned within apocket 49 defined by cap 48 and differential case 40. Actuator assembly50 is selectively energizable to cause dogs 86 of actuating ring 54 toengage dogs 215 of side gear 204. Differential assembly 200 functionssubstantially similarly to differential assembly 26 in that it is placedin a locked mode when dogs 86 engage dogs 215. The differential assemblycan be placed in an open mode by discontinuing current supply to coil96. Compression spring 85 axially displaces actuator assembly 50 tocause dogs 86 to disengage from dogs 215.

While a rear drive axle assembly has been described in detail, it shouldbe appreciated that the differential system of the present invention isnot limited to such an application. Specifically, the differentialsystem of the present invention may be used in transaxles forfront-wheel drive vehicles, transfer cases for use in four-drivevehicles and/or a number of other vehicular driveline applications.

FIGS. 7, 10 and 11 depict another alternate embodiment differentialassembly 300. Differential assembly 300 is substantially similar to thepreviously described differential assemblies except that differentialassembly 300 includes an alternate embodiment actuator assembly 302. Forclarity, like elements will retain the previously introduced referencenumerals.

Differential assembly 300 alleviates the need for washer 112 that waspreviously positioned between actuator assembly 50 and cap 48. FIGS. 8and 9 depict washer 112 of differential assemblies 26 and 200. Aspreviously mentioned, washer 112 is constructed from a non-magnetizablematerial such as aluminum to reduce the tendency for the magnetizableactuating ring 54 to be attracted toward metallic cap 48 instead ofdifferential case housing 40 during energization of solenoid assembly52.

FIGS. 10 and 11 depict actuator assembly 302 for use with differentialassembly 300. Actuator assembly 302 includes an actuating ring 304 witha plurality of pads 306 coupled to actuating ring 304. Actuating ring304 is substantially similar to actuating ring 54. Specifically,actuating ring 304 includes a generally hollow cylindrical body 78having annular recess 80 formed at one end. Dogs 86 axially extend fromend face 88. Actuating ring 304 is preferably constructed from amagnetizable material. Magnetizable materials include at least thoseclassified as ferromagnetic and ferrimagnetic. Actuating ring 304includes a substantially planar surface 308 having three radiallyextending portions 310 interconnected by substantially circular portion312. An aperture 314 extends through each radially extending portion310. Apertures 314 are preferably internally threaded for receipt offasteners 110. Pads 306 are depicted in FIG. 11 as substantiallyrectangular blocks coupled to radially extending portions 310. Pads 306may be constructed from any number of non-magnetizable materialsincluding plastic, rubber or another polymer. The pads may be affixed toplanar surface 308 by a gluing operation or pads 306 may be molded toactuator ring 304. Although pads 306 are depicted as individually spacedapart elements in FIG. 11, it is within the scope of the presentinvention to use a one-piece spacer coupled to planar surface 308. Theone-piece spacer may be adhesively bonded to or molded to actuator ring304.

The use of a polymer spacer or pads coupled to actuating ring 304defines a cost reduced differential assembly compared to an assemblyusing a separate aluminum washer. Furthermore, because the spacer orpads 306 are coupled to actuating ring 304, fewer parts need to beinventoried, handled and assembled. By integrating the spacer andactuating ring into a unitary assembly, the tendency for an assembler toinadvertently eliminate a component is reduced.

In operation, spacer or pads 306 provide a minimum spacing betweenplanar surface 308 of actuating ring 304 and end face 74 of cap 48. Thisminimum spacing assures that coil 96 generates an attracting forceattempting to move actuating ring 304 toward the engaged position thatis greater than the force supplied by spring 85 plus the forceattempting to move actuating ring 304 toward the disengaged position.Accordingly, actuator assembly 302, including actuating ring 304, movesfrom the disengaged position to the engaged position when coil 96 isenergized.

Furthermore, the foregoing discussion discloses and describes merelyexemplary embodiments of the present invention. One skilled in the artwill readily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationsmay be made therein without department from the spirit and scope of theinvention as defined in the following claims.

1. A differential system comprising: a rotatable case defining aninterior cavity; a pair of pinion gears rotatably supported in saidinterior cavity; a pair of side gears rotatably supported in saidinterior cavity, wherein each of said pinion gears drivingly engageseach of said side gears; and an electrically operable coupling includinga moveable electromagnet and a non-magnetic spacer coupled thereto, saidcoupling being operable to selectively connect one of said side gears tosaid case in response to movement of said electromagnet toward said sidegears, said spacer positioning the electromagnet to reduce a forceurging said coupling away from said side gears.
 2. The differentialsystem of claim 1 wherein said spacer limits the travel of said couplingaway from said side gears.
 3. The differential system of claim 2 furtherincluding a ring selectively engageable with said one of said sidegears, said ring being rotationally retained by said case and axiallymoveable relative to said case.
 4. The differential system of claim 3wherein said case includes a removable cap, said spacer being positionedbetween said cap and said ring.
 5. The differential system of claim 4wherein said cap includes a recess within which a portion of saidcoupling is positioned.
 6. The differential system of claim 5 furtherincluding a spring biasing said ring toward a position disengaged fromsaid first side gear.
 7. The differential system of claim 6 wherein saidpinion gears rotate about a first common axis and wherein said first andsecond side gears rotate about a second common axis, said first commonaxis being positioned substantially orthogonal to said second commonaxis.
 8. The differential system of claim 6 wherein said pinion gearsrotate about axes parallel to and offset from one another.
 9. Thedifferential system of claim 1 wherein said case includes a portionpositioned on an opposite side of said coupling as said pair of sidegears, wherein during energization of said electromagnet, saidelectromagnet is attracted toward said portion of said case by a forceless than a force attracting said electromagnet toward said side gears.10. A differential system comprising: a case defining an interiorcavity, said case having a bore communicating with said interior cavity;a pair of pinion gears positioned within said interior cavity androtatably coupled to said case; first and second side gears positionedwithin said interior cavity in meshing engagement with said pinion gearsand rotatably coupled to said case; an electromagnetic actuator having acoil moveable within said bore between an engaged position and adisengaged position, said case being drivingly coupled to said firstside gear when said coil is in said engaged position; a spring biasingsaid actuator toward said disengaged position; and a spacer coupled tosaid actuator, said spacer defining the position of said actuatorrelative to said engaged position, wherein a force attracting saidactuator toward said engaged position is greater than a force providedby said spring and a force attracting said actuator toward saiddisengaged position such that said actuator moves toward said engagedposition when an electrical current is passed through said coil.
 11. Thedifferential system of claim 10 wherein said electromagnetic actuatorincludes an axially slidable ring coupled to said coil, said ring beingselectively engageable with said first side gear.
 12. The differentialsystem of claim 11 wherein said spacer is integrally molded to said ringto define a unitary component.
 13. The differential system of claim 11wherein said ring includes a plurality of dogs that are selectivelyengageable with a plurality of dogs extending from said first side gear.14. The differential system of claim 11 wherein said spacer includes aplurality of spaced apart pads coupled to said ring.
 15. A differentialsystem comprising: a rotatable case defining an interior cavity; a pairof pinion gears rotatably supported in said interior cavity; a pair ofside gears rotatably supported in said interior cavity, wherein each ofsaid pinion gears drivingly engages each of said side gears; and anelectrically operable coupling including a moveable electromagnet and anon-magnetic spacer coupled thereto, said coupling being operable toselectively connect one of said side gears to said case in response tomovement of said electromagnet, said spacer maintaining at least apredetermined distance between said coupling and a magnetizable portionof said case.
 16. The differential system of claim 15 wherein saidmagnetizable portion of said case is positioned on an opposite side ofsaid coupling as said pair of side gears.
 17. The differential system ofclaim 16 wherein said coupling includes an axially slidable ringengageable with one of said side gears and wherein said spacer iscoupled to said ring.
 18. The differential system of claim 17 whereinsaid spacer includes a plurality of spaced apart pads coupled to saidring.
 19. The differential system of claim 18 further including a springbiasing said ring toward a position disengaged from one of said sidegears.
 20. The differential system of claim 19 wherein said spacer isengaged with said magnetizable portion of the case when said ring is insaid position disengaged from one of said side gears.
 21. Thedifferential system of claim 17 wherein said spacer is molded to saidring to define a unitary member.